Tablets have been extensively used in a field which is not related to detergent or dishwashing detergent arts, namely, in a field of medicine. In addition to producing uniform tablets, pharmaceutical industry has attempted to solve a problem of incorporating two substances which are incompatible with one another in the same tablet. In some cases, it is desired that a medicinal tablet release the same or different actives at successive times. A tablet for pharmaceutical use which is able to release an active substance at successive times is disclosed by Conte et al., U.S. Pat. No. 4,865,849. The tablet of the Conte et al. patent is said to be particularly suitable in medicinal field but generally usable in all sectors in which active substances have to be released at different times spaced apart by a predetermined time interval such as in the fertilizer, herbicide and other sectors.
The tablet of Conte et al. includes a first layer containing a portion of the active substance and suitable excipients, a barrier layer of polymer material, and a third layer containing the remaining portion of active substance or another active substance. The barrier layer and the third layer are housed in a casing. For the barrier layer, polymers are used which are gellable and/or soluble on contact with water or aqueous fluids. The polymers for the barrier layer of the tablet disclosed by Conte et al. are chosen from cellulose derivatives such as hydroxypropylmethylcellulose, methylcellulose or polyvinylalcohols of various molecular weights. For the casing, water-insoluble materials are preferably used, but in certain embodiments polymers soluble in an alkaline environment can be used to facilitate destruction of the casing when in the enteric tract.
A multistage release pharmaceutical tablet having a structure similar to the tablet disclosed by Conte et al. is described in Great Britain patent application 1,346,609.
The structure of the tablet disclosed by the Conte et al. patent and the '609 reference differs from a structure of a tablet taught by the present invention. In the tablet disclosed by Conte et al. and by the '609 reference, the first and the third layer each contact only one side of a barrier layer. Consequently, all layers of the tablet disclosed by the Conte et al. patent and the 609 reference would be exposed to water simultaneously and the tablet requires an additional, fourth layer which is needed to encase the barrier layer and the third layer. By contrast, in the tablet of the present invention an outer layer encloses a barrier layer on all sides, and the barrier layer, in turn, encloses an inner layer on all sides.
Although the tablet of the Conte et al. patent is said to be suitable for use in fields other than medicinal field, the Conte et al. patent and the '609 reference neither mention dishwashing nor disclose problems of providing sequential release under conditions of machine dishwashing cleaning which include high agitation, high temperature, highly alkaline cleaning environment and a strict time cycle program.
In this regard, it should be noted that while a sequential release is a feature of some medicinal tablets and the dishwashing detergent tablet of the present invention, the chemical composition and physical characteristics of the two tablets are so different, the release time program and the environment of dissolution are so diverse, and the principles and skills required in formulating the two tablets are so distinct, that it is difficult to extend the teachings in one of the arts to the other.
In the dishwashing and detergent arts, cleaning compositions in tablet form have been described, for example, in U.S. Pat. No. 3,318,817 to Smith, in U.S. Pat. No. 3,329,615 to Cooper et al., U.S. Pat. No. 3,344,076 to Wilcox, U.S. Pat. No. 3,417,024 to Goldwasser, U.S. Pat. No. 3,390,092 to Keast et al., U.S. Pat. No. 3,488,420 to Keast et al., U.S. Pat. No. 4,219,435 to Biard et al., U.S. Pat. No. 4,219,436 to Gromer, and U.S. Pat. No. 4,587,031 to Kruse et al., the '092, '435, '436 and '031 patents being directed particularly to dishwashing tablets. It has been disclosed that the use of detergent tablets may be advantageous, since the tablets are nondusting, do not require measuring, take less space because they are compressed, and ingredients of the tablets do not segregate on storage. However, all of the above cited patents disclose tablets which are uniform in composition and there remain dishwashing formulation problems which have not been addressed by these patents. Among the unsolved problems is a problem of incompatibility of various dishwashing detergent ingredients.
For example, it has been found that it is particularly beneficial to include both an enzyme and a chlorine bleach in order to achieve better cleaning of dishware. Unfortunately, enzymes are deactivated in the presence of the chlorine bleach, during storage and in an aqueous cleaning solution formed in a dishwashing machine. Enzyme-containing dishwashing compositions are generally formulated with oxygen bleaches, such as perborate, in place of chlorine. However, it has been found that dish cleaning performance of oxygen bleaches is far inferior to dish cleaning performance of chlorine bleaches. Other examples of incompatible ingredients include surfactants, dyes and perfumes all of which, unless specially selected, are incompatible with chlorine.
Elrich, U.S. Pat. No. 4,099,912 and Elrich, U.S. Pat. No. 4,253,842 disclose that components of detergent compositions can be separately tableted. It is evident that such separately tableted formulations make it necessary for a consumer to purchase a large number of different tablets in order to arrive at a complete effective formulation. Additionally, unless various incompatible components are introduced into a dishwashing machine as separate tablets at successive time intervals (which would be extremely inconvenient), there still exists the problem of deactivation of the incompatible components in an aqueous cleaning environment of a dishwashing machine once the tablets have been dissolved.
U.S. Pat. No. 4,839,078 to Kruse et al. discloses detergent tablets having a uniform composition and a broad solubility profile: at least 10% of the tablet is dissolved in only the prerinse cycle by the cold water flowing in, and at least 65%, preferably at least 70%, by weight of the tablet is available for the main wash cycle due to its good solubility in warm water. The tablet of Kruse et al. contains alkaline-reacting components such as alkali metal metasilicates and penta-alkali metal triphosphates, active chlorine compounds and tableting aids.
Jeschke et al., U.S. Pat. No. 4,828,745, Kruse et al, U.S. Pat. No. 4,828,749 and Kruse et al., U.S. Pat. No. 4,913,832 disclose multilayer dishwashing tablets which are suitable for simultaneous use in the pre-rinse cycle and in the main wash cycle of dishwashing machines. The '745 patent discloses a block-form detergent which includes two or more differently acting layers fused to each other. The first layer is cold water soluble and the second layer is warm water soluble. The '745 patent mentions that the layer formation disclosed therein may be used for the separation of incompatible components. The '749 patent discloses a multilayer detergent tablet similar to the block-form detergent of the '745 patent. The first layer is cold water soluble and includes a nonionic surfactant. The second layer is warm water soluble and includes an active chlorine compound. The '832 patent discloses a two-layer compact which may contain chlorine and nonionic surfactant provided that they are incorporated into different layers.
A serious shortcoming of the tablets disclosed in the Kruse et al. '078 patent, the Jeschke et al. '745 patent and the Kruse et al. '749 and '832 patents is that during storage incompatible ingredients are still in contact with each other in a border area, where two layers meet. An even more important shortcoming of the tablets disclosed in these patents is that it is not possible to provide a separate release of incompatible ingredients during the same cycle of dishwashing cleaning or during different cycles occurring at the same water temperature: both layers of the tablets are exposed to water simultaneously and, unless water temperature is different, dissolution of both layers occurs at the same time. Thus, if the first layer were to include an enzyme and the second layer were to include a chlorine bleach, the enzyme and the chlorine bleach would be dissolving at the same time. As a result, the enzyme would be deactivated by the chlorine bleach before the enzyme has had time to perform its cleaning function.
Fernholz et al., U.S. Pat. No. 4,569,780 and Fernholz et al., U.S. Pat. No. 4,569,781 describe a process for preparing a solid castdetergent, and a solid cast detergent produced by the process. Fernholz et al. disclose that the cast detergent article can be designed or structured to minimize chlorine stability and differential solubility problems, e.g. by including the chlorine source and/or the defoamer as preformed plugs or cores encased in the cast detergent composition. The cast detergent is surrounded on all but one surface by a disposable mold in which it was formed. To minimize reactivity between the base detergent and any material added as preformed plugs, the core material may be optionally encased in a film which would not react with the core material or the detergent base. The film materials disclosed are a natural wax, a synthetic wax, a phosphate ester, or the like. Examples 4 and 6 of the Fernholz et al. patents are cast detergent articles containing chlorine and/or defoamer plugs and Example 13 describes improved storage stability of the cast detergent articles containing the plugs.
Although storage stability of the cast detergents containing incompatible ingredients disclosed by Fernholz et al. can be achieved by separating the incompatible ingredients, dissolution of the incompatible ingredients is not separated in time. Fernholz et al. disclose that in use water impinges on the exposed surface of the plug material and the detergent base; the base detergent and the plug material dissolve at substantially the same rate so that a constant ratio of components can be maintained during use.
Thus, in formulating automatic dishwashing detergent tablets, it has been necessary to avoid a co-presence of various incompatible ingredients (such as a chlorine bleach and an enzyme) which deactivate each other in use. At best, the ingredients have been selected which are more compatible but not as efficient with regard to performance or cost as desired. It should be emphasized that merely separating incompatible ingredients during storage, albeit important, is not sufficient It is essential that dissolution of the ingredients is separated in time so that during use sufficient time is allowed for one of the ingredients (e.g., enzyme) to perform its function prior to a release of the second ingredient (e.g., chlorine) which deactivates the first one.
In addition to the incompatibility problems, dishwashing tablets which are able to release sequentially components contained therein are needed for other reasons. For example, it has been established that a rinse aid greatly improves appearance of dishes and glasses by decreasing the amount of spotting and filming and improving the shining of dishes and glasses. Heretofore, it has been necessary to introduce the rinse aid in a dishwashing machine separately from a dishwashing detergent, which is inconvenient and requires a separate purchase by a consumer. Moreover, many consumers are not yet aware of benefits associated with the use of the rinse aid and, thus, omit the use of the rinse aid entirely. By incorporating the rinse aid directly into an autodish detergent and having it released only in the final rinse, it could be ensured that glass appearance is enhanced without a need for a separate use or purchase of the rinse aid by a consumer.
Accordingly, it is an object of the present invention to provide a dishwashing detergent tablet which delivers convenience and improved cleaning performance in addition to improved storage stability.
It is another object of the present invention to provide a dishwashing detergent tablet which releases sequentially ingredients contained therein.
It is yet another object of the present invention to provide a dishwashing detergent tablet which contains both an enzyme and a chlorine bleach.
It is yet another object of the present invention to provide a dishwashing detergent tablet which releases an enzyme prior to a release of a chlorine bleach, and which releases the chlorine bleach after the enzyme had sufficient time to perform its cleaning function in an aqueous cleaning environment of a dishwashing machine.
It is still another object of the present invention to provide a dishwashing detergent tablet which contains both a dishwashing detergent composition and a rinse aid and which releases the rinse aid after detergent cleaning has been accomplished.
It is still another object of the present invention to provide methods of dishwashing by the use of the tablets disclosed herein.
Other objects and advantages will appear as the description proceeds.